ffmpeg_opt: Parse regular options in `ffpreset` files

instead of only AV-specific options. The previous code assumed that any
option not defining the codec in an `ffpreset` file is an AVOption. This
for example prevented the use of options defined in `OptionDef[]`, like
`-pix_fmt`, as part of preset files, requiring users to type these out
every time.

Closes: #1530
Signed-off-by: Andreas Hartmann <hartan@7x.de>

fftools/ffmpeg_opt.c

@@ -1050,7 +1050,8 @@ static int opt_preset(void *optctx, const char *opt, const char *arg)
         else if (!strcmp(key, "vcodec")) opt_video_codec   (o, key, value);
         else if (!strcmp(key, "scodec")) opt_subtitle_codec(o, key, value);
         else if (!strcmp(key, "dcodec")) opt_data_codec    (o, key, value);
-        else if (opt_default_new(o, key, value) < 0) {
+        else if ((parse_option(o, key, value, options) < 0) &&
+                 (opt_default_new(o, key, value) < 0)) {
             av_log(NULL, AV_LOG_FATAL, "%s: Invalid option or argument: '%s', parsed as '%s' = '%s'\n",
                    filename, line, key, value);
             ret = AVERROR(EINVAL);